Abstract
Understanding who does what to whom is at the core of sentence comprehension. The actors that contribute to the verb meaning are labeled thematic roles. We used transcranial magnetic stimulation (TMS) to verify the possible impact of verb semantics on the thematic role encoding process that has been shown to involve the posterior portion of the left posterior parietal sulcus (PPS; Finocchiaro et al., 2015). Sixteen participants underwent TMS and sham stimulation sessions while performing an agent-decision task, in which they had to decide by key press which of the two arguments was the agent of visually presented sentences or pseudo-sentences. The (pseudo)sentences were all reversible and were presented in the active or passive diathesis. Double pulse TMS was delivered to the posterior part of the intraparietal sulcus in an event-related fashion, at two different time windows: 200-400 ms (T1) or 600-800 ms (T2) time-locked to the presentation of the (pseudo)sentence. Results showed that TMS increased accuracy on passive sentences and pseudo-sentences as compared to active sentences and to the baseline, sham condition. Indeed, the presence of a verb with a full semantic representation was not a necessary precondition for the TMS-induced facilitation of passive (pseudo)sentences. Stimulation timing had no effect on accuracy for sentences vs. pseudo-sentences. These observations support the idea that the posterior parietal site is recruited when the correct interpretation of a sentence requires reanalysis of temporarily encoded thematic roles (as in reversible passive sentences) even when the verb is not an entry in the lexicon and hence does not have a semantic representation. Results are consistent with previous evidence and deserve further investigation in larger experimental samples. Increasing the number and variety of stimulus sentences, and administering TMS to additional control sites will be key to further articulate the conclusions allowed by these initial findings.
Highlights
The ability to understand who does what to whom is a core function of sentence comprehension
The most credited linguistic accounts posit the involvement of verb semantics in thematic role encoding (Dowty, 1989, 1991; Lebani et al, 2015; Levin & Rappaport Hovav, 2005; McRae et al, 1997; Van Valin, 1999)
It should be noted that the main contrast on which our results are based is the comparison between the effects of effective transcranial magnetic stimulation (TMS) applied to one single spot with the effects of sham TMS
Summary
The ability to understand who does what to whom is a core function of sentence comprehension. When a transitive verb is used in the active diathesis, the thematic role of its arguments (agent and theme, respectively) matches their syntactic function (subject and object, respectively). The same event as Judith bites the apple can be described by the passive sentence The apple is bitten by Judith. The apple is the subject of the sentence, but its thematic role is the same as in the active sentence (i.e., theme) as the apple does not start the bitingaction but is still the element that undergoes biting. Claire is both the object and the theme but, when the sentence is transformed in the passive diathesis (Claire is bitten by Judith), Claire becomes the grammatical subject while remaining the logical theme
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